How to copy weight paint to other arms
A bone moves vertices that have a vertex group weight that matches the bone name.

Starting with the weight painted arm, in edit mode select the arm and use P->separate by selection. In object mode, duplicate the new arm object and move it into position for another arm. Rename the vertex groups in the duplciate arm to match the corresponding arm bones, eg. rename arm1_upper to arm2_upper. Repeat for each arm.

In the original mesh, delete the arm meshes. In object mode, select all the arms and then the body, use &#9096; CtrlJ to join them into one mesh. Each arm bone should now move the matching arm.